And I'm Melissa Block. The battle for control of eastern Ukraine heated up again today. Pro-Russian insurgents shot down a military helicopter - killing at least a dozen soldiers, including an Army general. The deaths came days after the Ukrainian military inflicted heavy losses on rebels, who had seized the Donetsk airport.

This latest incident again calls into question the ability of Ukrainian government to suppress the revolt, which Ukraine's president-in-waiting says must happen as soon as possible. NPR's Peter Kenyon joins us now from Kiev. And Peter, first, what can you tell us about the downing of that helicopter?

PETER KENYON, BYLINE: It happened during fighting around the pro-Russian stronghold of Sloviansk. The first official word came from the acting president, Oleksandr Turchynov. He confirmed to the parliament that Army General Serhiy Kulchysky was among the soldiers killed. Turchynov said militants used a handheld anti-aircraft unit to bring down the helicopter.

It's the worst loss for the military since 14 servicemen were ambushed at a checkpoint in the east earlier this month. Later in the day, the National Guard said the site where the attack was launched was hit and destroyed by the military. But we don't have any confirmation that the attackers were still there at that point.

BLOCK: Peter, Turchynov also said that rebels used Russian-made portable surface-to-air missiles to shoot down this helicopter. Can we conclude, from that, that the Russian government is in fact arming the rebels or no?

KENYON: Well, we haven't confirmed yet - Mr. Turchynov's assertion that it was a Russian surface-to-air missile, in this incident. But Russian weapons and gear are turning up all over this conflict. There's even a group calling itself the Vostok Battalion. They openly admit to being Russian citizens. They claim they were trained by the Russian military before coming across the border.

In general, I'd say one shot with the service-to-air missile - whoever made it won't change the course of the conflict- but it has revived this conversation about whether the government is capable of putting down this rebellion at all, let alone quickly. Yesterday, a former head of Ukrainian intelligence was telling a number of reporters about long-term structural shortcomings and strategic problems that began under the former president, Yonukovych. And that can't be corrected overnight.

The military did inflict some big losses on the rebels Monday night at the Donetsk airport - possibly as many as 100 fighters killed, according to some rebels. But even then, it was clear they were lacking the manpower or the will, perhaps, to control the neighborhoods around the airport, where the fighting continued. For Russia's part, it says there's no official involvement in this conflict, although they did say volunteers may be crossing the border. And we know that's happened before in Georgia and elsewhere.

BLOCK: Well, Russia also has stepped up its rhetoric. It's called on Ukraine to stop what it's calls a fratricidal war and start a dialogue. What do you make of that demand?

KENYON: This has been their theme for some time now- dialogue between Kiev and the east. That seems unlikely in the short term. Although officials and analysts here do say they would love to talk with ordinary citizens in the east, they are just not eager to sit down with the armed separatist, who they consider criminals.

BLOCK: And, Peter, the Ukrainian president elect Petro Poroshenko is supposed to be sworn in just over a week from now, Peter. Is that likely to have an impact on the situation in the east?

KENYON: Well, that is a big question. The man Poroshenko will be replacing, acting president, Oleksandr Turchynov, says the swearing-in will be taking place on June 7- probably with the ceremony at Kiev's Independence Square. We're hearing Russian President Vladimir Putin has not been invited. We'll see if he is before the day arrives. Now, Poroshenko actually assuming power will certainly give some momentum to this notion that Ukraine is turning a corner - gaining some legitimacy.

It will not, however, make the challenges facing the country any easier. Right now, Mr. Poroshenko is getting strong approval from Ukrainians for taking a hard line against the insurgents. But if this turns into a drawn out conflict with significant civilian losses, a lot of that goodwill may evaporate quite fast.